1. Field of the Invention
The present invention relates to a technology for reproducing video data and audio data received via a network.
2. Description of the Related Art
Communication system are know in the art that can transmit video data or audio data (hereinafter, “multimedia data”) to other device on a network, receive multimedia data from other device on a network and reproduce the received data. In such a communication system, a communication device on the transmitting side (hereinafter, “transmitting device”) transmits multimedia data to a communication device on the receiving side (hereinafter, “receiving device”). In this configuration, however, it is necessary to accurately synchronize the operating clocks of the transmitting device and the receiving device.
Japanese Patent Application Laid-Open No. H11-308203 discloses a first conventional technology for synchronizing operating clocks between the transmitting device and the receiving device. In the first conventional technology, the transmitting device multiplexes time information on the multimedia data and transmits the time-information-multiplexed multimedia data to the receiving device.
Japanese Patent Application Laid-Open No. 2006-148227 discloses a second conventional technology for synchronizing operating clocks between the transmitting device and the receiving device. In the second conventional technology, the receiving device temporarily stores the multimedia data received from the transmitting device in a buffer, and adjusts its own operating clock by monitoring a usage of the buffer.
The first conventional technology requires that the time information be transmitted at accurate time intervals. However, in typical networks, such as the Internet, sometimes there are large variations in data transmission timings (hereinafter, “jitter”). If such a jitter occurs, time information can not be transmitted at accurate time intervals, so that problems such as image jump, color drift, audio delay, and audio traverse occur.
In the second conventional technology, the multimedia data is first stacked in a buffer and the multimedia data is read from the buffer while adjusting the operating clock. Thus, there is higher possibility of correcting the operating clocks because the buffer can function as an agent to absorb the jitter to some extent. The second conventional technology, however, can not cope with larger jitters.